While "frequent" would probably be an exaggeration when it comes to describing Gmail outages, "unusual" might be missing the mark by a hair, too. In the past six months, Gmail has suffered some form of downtime on five separate occasions before this week's incident:

• : A similar "502 error" struck Gmail, leading to what was described as a "long outage" by affected users.

• : Technical trouble knocked an "undetermined number" of Gmail users (including both regular users and paying Google Apps clients) out of their mail for about 15 hours.

• : An issue with Google's "contacts system" caused Gmail access to go offline for a "couple of hours" for numerous users. Both individual accounts and Google Apps accounts were affected again.

• : The third outage within a span of two weeks left users locked out of their accounts for more than 24 hours. That pesky "502 server error" popped up on the Gmail login page here, too.